1. Field of the Invention
This invention relates to an iron-based amorphous alloy with a saturation induction exceeding 1.6 Tesla and adapted for use in magnetic devices, including transformers, motors and generators, pulse generators and compressors, magnetic switches, magnetic inductors for chokes and energy storage and sensors.
2. Description of the Related Art
Iron-based amorphous alloys have been utilized in electrical utility transformers, industrial transformers, in pulse generators and compressors based on magnetic switches and electrical chokes. In electrical utility and industrial transformers, iron-based amorphous alloys exhibit no-load or core loss which is about ¼ that of a conventional silicon-steel widely used for the same applications operated at an AC frequency of 50/60 Hz. Since these transformers are in operation 24 hours a day, the total transformer loss worldwide may be reduced considerably by using these magnetic devices. The reduced loss means less energy generation, which in turn translates into reduced CO2 emission.
For example, according to a recent study conducted by International Energy Agency in Paris, France, an estimate for energy savings in the Organization for Economic Co-operation and Development (OECD) countries alone that would occur by replacing all existing silicon-steel based units was about 150 TWh in year 2000, which corresponds to about 75 million ton/year of CO2 gas reduction. The transformer core materials based on the existing iron-rich amorphous alloys have saturation inductions B, less than 1.6 Tesla. The saturation induction B5 is defined as the magnetic induction B at its magnetic saturation when a magnetic material is under excitation with an applied field H. Compared with Bs˜2 Tesla for a conventional grain-oriented silicon-steel, the lower saturation inductions of the amorphous alloys leads to an increased transformer core size. It is thus desired that the saturation induction levels of iron-based amorphous alloys be increased to levels higher than the current levels of 1.56-1.6 Tesla.
In motors and generators, a significant amount of magnetic flux or induction is lost in the air gap between rotors and stators. It is thus desirable to use a magnetic material with a saturation induction or flux density as high as possible. A higher saturation induction or flux density in these devices means a smaller size device, which is preferable.
Magnetic switches utilized in pulse generation and compression require magnetic materials with high saturation inductions, high BH squareness ratios defined as the ratios of the magnetic induction B at H=0 and Bs, low magnetic loss under AC excitation and small coercivity Hc which is defined as the field at which the magnetic induction B becomes zero, and low magnetic loss under high pulse rate excitation. Although commercially available iron-based amorphous alloys have been used for these types of applications, namely in cores of magnetic switches for particle accelerators, Bs values higher than 1.56-1.6 Tesla are desirable to achieve higher particle acceleration voltages which are directly proportional to Bs values. A lower coercivity Hc and a higher BH squareness ratio mean a lower required input energy for the magnetic switch operation. Furthermore a lower magnetic loss under AC excitation increases the overall efficiency of a pulse generation and compression circuit. Thus, clearly needed is an iron-based amorphous alloy with a saturation induction higher than Bs=1.6 Tesla, with Hc as small as possible and the squareness ratio B(H=0)/Bs as high as possible, exhibiting low AC magnetic loss. The magnetic requirements for pulse generation and compression and actual comparison among candidate magnetic materials was summarized by A. W. Melvin and A. Flattens in Physical Review Special Topics-Accelerators and Beams, Volume 5, 080401 (2002).
In a magnetic inductor used as an electrical choke and for temporary energy storage, a higher saturation induction of the core material means an increased current-carrying capability or a reduced device size for a given current-carrying limit. When these devices are operated at a high frequency, core material must exhibit low core losses. Thus, a magnetic material with a high saturation induction and a low core loss under AC excitation is preferable in these applications.
In sensor applications of a magnetic material, a high saturation induction means a high level of sensing signal, which is required for a high sensitivity in a small sensing device. Low AC magnetic losses are also necessary if a sensor device is operated at high frequencies. A magnetic material with a high saturation induction and a low AC magnetic loss is clearly needed in sensor applications.
In all of the above applications which are just a few representatives of magnetic applications of a material, a high saturation induction material with a low AC magnetic loss is needed. It is thus an aspect of this invention to provide such materials based on iron-based amorphous alloys which exhibit saturation magnetic induction levels exceeding 1.6 T and which are close to the upper limit of the commercially available amorphous iron-based alloys.
Attempts were made in the past to achieve an iron-based amorphous alloy with a saturation induction higher than 1.6 T. One such example is a commercially available METGLAS®2605CO alloy with a saturation induction of 1.8 T. This alloy contains 17 at. % Co and therefore too expensive to be utilized in commercial magnetic products such as transformers and motors. Other examples include amorphous Fe—B—C alloys as taught in U.S. Pat. No. 4,226,619. These alloys were found mechanically too brittle to be practically utilized. Amorphous Fe—B—Si-M alloys where M=C as taught in U.S. Pat. No. 4,437,907 were intended to achieve high saturation inductions, but were found to exhibit Bs<1.6 T.
Thus, there is a need for ductile iron-based amorphous alloys with saturation induction exceeding 1.6 T, having low AC magnetic losses and high magnetic stability at devices' operating temperatures.